I started growing and selling wheat grass this year (photos I posted were taken last summer). People here buy it for smoothies and also for their pets - some cats and dogs apparently love both wheat and oat grass.
If I had a license from the health dept, I could bring a juicer and offer wheat grass "shots" at the market. But I don't want to spend the $ on a fancy juicer right now. The grocery store dried peas are more expensive for me than the garden peas. I buy the peas in 100 lb amounts when I need them, so they end up being my cheapest crop to buy. For somebody growing at home, it won't cost you much to start growing greens.